Evaluate the following expression when $b = 3$ and $a = 3$. $6$ $b$ $ + 9$ $a$ $ - 7$
Answer: Substitute $3$ for ${b}$ and $3$ for ${a}$ $ = 6{(3)} + 9{(3)} - 7 $ $ = 18 + 27 - 7 $ $ = 38$